The present invention relates to the field of vacuum cleaner fans. In a conventional vacuum cleaner, a fan drives dirt-laden air into a filter bag. There are two common vacuum cleaner configurations. In a "dirty-air" type vacuum cleaner, the fan is positioned before the filter bag and pushes dirt-laden air into the filter bag. In a "clean air" type vacuum cleaner, the fan is positioned after the filter bag and sucks clean air out of the filter bag, drawing the dirt-laden air into the bag.
FIG. 1 shows a conventional dirty-air vacuum cleaner 10. A fan 12 draws air through a floor nozzle 14 to a filter bag 16 by way of a fill tube 18. Dirt removed from the floor by the airflow is thus filtered out and deposited into the filter bag 16. FIG. 2 is a front sectional view of the fan 12, illustrating its principle of operation. A motor 20 is connected to the back of housing 22 and rotates the impeller 24 with a shaft 26. The resulting centrifugal force draws air into an inlet 28 and propels the air outwardly through an outlet 30.
FIG. 3A shows a detailed perspective view of the impeller 24, which is representative of the type of impeller commonly used in dirty-air vacuum cleaners. A conventional impeller 24 comprises a hub 42 supporting a backplate 44 which supports multiple blades 46. The hub 42 has a bore 48 for mounting onto the motor shaft 26. The empty area between the hub 42 and the blades 46 is called the "eye" 49 and is used to provide more space for air entering the inlet 28. The backplate 44 is curved, as shown in FIG. 3B, to reduce the right angle turn encountered by the airflow when it first hits the fan. Also, the blades 46 are typically not aligned radially, but are backswept relative to the rotational direction. Blades 46 are usually curved, as shown in FIG. 3A. The above-indicated design features are incorporated into the impeller design to improve air performance (in terms of suction and airflow) and also reduce fan noise. However, such conventional impellers also suffer from certain drawbacks.
A typical vacuum cleaner impeller is made of rigid material, such as aluminum or polycarbonate. Being rigid, such impellers are prone to damage from fast rotation. In order to establish the airflow required for removing dirt, an impeller must be rotated at high speed, typically 10,000-20,000 RPM. The strong centrifugal force acting on the impeller's mass stresses the curved backplate to pull away from the blades. This centrifugal force also stresses the blade curvature to radially straighten out and causes the backswept blades to tip over toward the backplate. The repeated on-off application of these stresses can produce stress cracks in the backplate and weaken the joint between blade and backplate. These stresses also gradually deform the blade shape and fatigue the impeller material. This damage reduces air performance and the durability of the impeller and increases noise level.
Besides centrifugal damage, there is also shrapnel damage. The impeller can be cracked when hard objects such as stones and bolts are picked up by the vacuum cleaner and hit the impeller with a violent impact. Due to the fast RPM, the imbalance caused by even slight cracks produces excessive vibration, noise, and bearing wear.
Another problem with conventional fans is their RPM limit. Fan size could be reduced without decreasing air performance by increasing the rotational speed. However, a conventional impeller cannot withstand the centrifugal force beyond a certain RPM limit.
In order to increase durability from shrapnel and stress cracking, conventional plastic impellers are reinforced by thickening the backplate and blades. But this solution is inefficient, since the additional mass further increases centrifugal stress, additionally increases manufacturing cost, and reduces the volume available for airflow.
In a conventional vacuum cleaner fan, the impeller diameter is larger than the inlet diameter. Since it will not fit through the inlet, installing or replacing the impeller requires dismantling the fan housing. This typically requires professional servicing, entailing expense and inconvenience due to unavailability of the vacuum cleaner.